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Error in using fitlnm: Why do I get "The model function must accept two arguments"?

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pietro
pietro on 16 May 2018
Commented: Star Strider on 16 May 2018
Hi all,
I am having troubles in using fillnm. Below an example:
clear all
x=[0:0.01:10];
y=x.^2;
modelfun=@(x)(x.^2);
beta0=1;
mdl=fitnlm(x,y,modelfun,beta0);
Unfortunately, I get the following error:
Error using classreg.regr.NonLinearFormula (line 225)
The model function must accept two arguments.
Error in NonLinearModel/createFormula (line 1643)
formula =
classreg.regr.NonLinearFormula(modelDef,coefNames,predictorVars,responseVar,varNames,ncoefs);
Error in NonLinearModel.fit (line 1397)
model.Formula =
NonLinearModel.createFormula(supplied,modelDef,X,ncoefs,coefNames,
...
Error in fitnlm (line 94)
model = NonLinearModel.fit(X,varargin{:});
Why do I get this error?
Thanks.
Best regards,
Pietro

Accepted Answer

Star Strider
Star Strider on 16 May 2018
The function must express the model you are fitting in terms of a vector of parameters and the independent variable, with the parameter vector being the first argument, and the independent variable the second argument.
Ideally, your model would be something like:
modelfun = @(b,x) b(1) + b(2).*x.^2;
If you are estimating no parameters, it makes no sense to use any parameter estimation function.

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